For military applications it is known to provide so-called impact or inertial projectiles, i.e. projectiles which may be self-propelled or fired from a barrel-type weapon such as a cannon, which comprise at least one core of high-density metal adapted to function as a penetrator or armor-breaking or armor-piercing element.
The penetrator, which functions because of its high kinetic energy on impact with the armor to pierce or damage the latter without the use of an explosive, can be carried on or form part of a projectile having a plurality of such cores (see the commonly assigned copending application Ser. No. 949,067 filed 5 Sept. 1978), now abandoned but replaced by Ser. No. 412,794 of Aug. 23, 1982 the cores being designed to pierce the armor in succession.
An impact or inertial projectile differs from an active-head projectile in that the latter generally carries an explosive charge which detonates as the projectile contacts or approaches the target whereas the former utilizes merely its kinetic energy to penetrate the armor wall.
Multi-core penetrators as described in the aforementioned copending application can be used when the armor of the target is multilayer or laminated armor (a so-called multiple target or structured target) in which case the successive engagement of cores with the armor permits penetration through successive layers and hence effective penetration into the vehicle or through the armor wall.
The core is, as noted, of a high-density hard metal and generally is surrounded by a shell which may be the casing of the projectile.
Behind the penetrator, the projectile may be provided with additional impact or inertial cores or with activatable charges which function once the projectile has penetrated the armor by explosion to destroy the target.
The high-density core of the penetrator, when surrounded by a lower-density metallic shell or casing, forms a penetrator of a median density, i.e. a density which is a weighted average of the densities of the core and the surrounding envelope of lighter metal.
This average density, of course, should be as high as possible since the penetration of the device is a function of the kinetic energy which, in turn, is a function of mass and the greater the density, the greater the mass for a given volume of the penetrator.
It is desirable that the mass be as large as possible of the core and this can be ensured by making the core elongated for a given diameter of the projectile so that the ratio of the length to the diameter of the core is relatively large. Such relatively elongated cores have been found to be especially effective against multilayer armor.
However, problems have been encountered when elongated cores were used.
For example, the cores are generally formed from a high-density hard material, e.g. tungsten, which is difficult to machine and hence the cores are formed by sintering and like powder-metallurgical techniques. lt has been found that when such cores engage the target and even when such cores are accelerated from the barrel of the weapon on firing of the projectile, they tend to crack transversely to their longitudinal dimension.
Such cracks can develop as a result of bending stresses applied during fabrication, assembly, firing or impact and are rapidly propagated through the core because the hard materials from which cores are made are generally relatively brittle so that the cracks customarily extend over the full cross section.
This results in a breakup of a core into pieces of small length and defeats the effort to provide a large length-to-diameter ratio.
ln some cases, the number of cracks and the degree of fragmentation of the core are so great that the penetrator totally loses its effectiveness or, at best, has significantly reduced penetration against multilayer targets.